Technical data

27
Heating system designs
System version 8 (continued)
Vitocontrol-S, VD2/CT3/CM2
Required coding
00: 3,
00: 4,
00: 7,
or
00: 8
Without system circuit A1
*1
35: 1
35: 2
35: 3
Vitocontrol-S, VD2/CT3/CM2 with
one Vitotronic 100, GC1
two Vitotronic 100, GC1
three Vitotronic 100, GC1
39: 1
to
39: 4
Setting up Vitocrossal 300 as permanent lead boiler
3b: 3 Autonomous series connection with supply temperature sensor
*1
If required.
Possible applications
For heating circuits with temperature differentials ≥20°C / 68°F
The Vitocrossal 300, CT3 (lead boiler) and the next Vitorond (lag boiler) are operated via a Viessmann control system with
outdoor reset logic, modulating boiler water temperature, and load-dependent sequential control – two-stage or modulating
burners are controlled.
Vitocrossal 300, CT3 is equipped with two return connections. The heating circuits with the higher return temperature are
connected to the upper return connection, and those with lower return temperatures to the lower return connection.
Please note: Connect at least 15% of the rated output to the lower return connection.
Temperature sensor T1 senses the return temperature.
The boiler control unit regulates the three-way mixing valve to ensure that the system never falls below the minimum return
temperature.
Due to the LON-BUS communication between controls, a boiler supply temperature is automatically set.
This temperature is based on the highest required mixing valve circuit temperature plus adjustable differential.
The connection diagram is only a
recommendation and needs to be
verified for completeness and
functionality at the installation site.
Single-phase and three-phase pumps
must be connected with field supplied
motor contactors and/or motor
starters.
5351 340 v1.4
IMPORTANT